Efficient Thermal Impedance Simulation of Insulated Gate Bipolar Transistors Modules on Heat Sinks

Abstract

The prediction of temperatures in power semiconductor modules, such as insulatedgate bipolar transistors (IGBTs) is critical to ensure adequate lifetime modeling of the devices. A temperature of particular interest is that of the semiconductor junction, which is used to assess the liftoff of wire bonds. For many applications featuring dynamic loads, the junction temperature needs to be simulated for socalled mission profiles of significant duration. To limit the computational expense, the simulations are based on thermal impedances from junction to ambient, which may be obtained from numerical 3d simulations. Even these 3d simulations can be computationally expensive. In powerelectronic systems, often, large heat sinks are used with a multitude of mounted IGBT modules, interacting thermally. In such cases, the detailed 3d models become large and the transient simulations are not feasible. In the present work, a method is proposed that allows us to significantly reduce the 3d model size. To this end, the ideas of compact or boundaryconditionindependent models are used. The presented method has the advantage that, unlike in modelorder reduction, the system matrices of the 3d model are not needed. This makes the method applicable to commercial simulation software like ANSYS Icepakâ„¢, that does not give access to the system matrices. The method is implemented via MATLABâ„¢ scripts that automatically generate 3d ANSYS Icepakâ„¢ models of IGBT modules on a heat sink. An example case of two IGBT modules mounted on an aircooled heat sink is presented, and the method is shown to yield good accuracy (thermalimpedance errors below 8% and thermalresistance errors close to zero), while reducing the model's mesh size by the factor of 14. Further error reduction is expected to be possible by adapting the model parameters. This can be subject to future work.